Vista - Service Pack 2 won't install - Please help

Hi,
I am running vista home premium and i have downloaded the service pack 2 download from the download centre. When i try to install it it tells me the following 'you must install windows vista service pack 1 before continuing'

i definately have pack 1 installed already but to make sure i tried to install it again and it said already installed.

Please help

What do you see in the system properties window:

If you have really SP1 installed and this error appear this means corruption or CBS key or in C:\Windows\Servicing\Packages folder.

1.Run cmd.exe with administrative previlliges (right click on cmd.exe) as admin and type:

sfc /scannow

When it finish type in cmd.exe

findstr /c:"[SR]" %windir%\logs\cbs\cbs.log >%userprofile%\Desktop\sfcdetails.txt

on your desktop appear sfcdetails.txt
2.Run Readiness Tool Description of the System Update Readiness Tool for Windows Vista, for Windows Server 2008, and for Windows 7
This tool even don't help create CheckSur.log file in C:\Windows\Logs\CBS

Both CheckSur.log and sfcdetails.txt please attache to post

Thanks,

I have run th sfc scan and the file it created on the desktop was blank.

I also downloaded the readiness tool and it ran an installation box (it didn't say scanning or anything) i presume this is right.
The checksur file was thee but again was blank

I presume this means there were no errors found?
When you go into the system menu it shows that i Have Vista service pack 1 installed.

Thanks

Very strange .Find CBS.log file in C:\Windows\LOGS\CBS pack it and attache to post.If this file will be too big to attache upload it on Speedy Share - upload your files here